1) Field of the Invention
The present invention relates to a polycarbonate resin composition excellent in chemical resistance and oil resistance, having low birefringence obtained by blending a polycarbonate resin derived from specific dihydroxy compounds and a polycarbonate resin from 2,2-bis(4-hydroxyphenyl) propane and to a polarizing sheet adhered a transparent sheet comprising the polycarbonate resin composition to a polarizing film.
2) Prior Art
A polycarbonate resin derived from 2,2-bis(4-hydroxyphenyl)propane (so-called bisphenol A) has been widely applied to optical materials including a base material of CD or DVD, optical films, optical sheets, various lenses and prisms since it is excellent in transparency, heat resistance, low water absorbing ability, chemical resistance, dynamic properties and dimensional stability. However, the polycarbonate resin derived from bisphenol A has a defect that it cannot be applied to the field to require low birefringence because it has a large photoelastic constant.
Thus, in the field to require low birefringence, an acrylic resin, an amorphous polyolefin or a polycarbonate resin with a particular structure have been used. However, for example, an acrylic resin has a defect that water absorbing degree is high and dimensional stability is poor. An amorphous polyolefin has defects that both impact resistance and chemical resistance are poor and it is expensive. Since each molded articles of an acrylic resin and an amorphous polyolefin have not always satisfactory low birefringence, these resins cannot be applied to the field to require further low birefringence.
As a polycarbonate resin with a particular structure, for example, Japanese Patent Kokai (Laid-open) No. 2000-169573 discloses a copolymerization polycarbonate resin derived from 9,9-bis(3-methyl-4-hydroxyphenyl)fluorene and tricyclo[5.2.1.02,6]decanedimethanol. Although an injection molded article comprising this resin exhibits sufficiently low birefringence, it has a defect that it is readily colored during production.
Further, as a polycarbonate resin with a particular structure, Japanese Patent Kokai (Laid-open) No. 10-101787 discloses a polycarbonate resin derived from 9,9-bis(4-(2-hydroxyethoxy)phenyl)fluorene. Although the polycarbonate resin has lower birefringence than that of a polycarbonate resin derived from bisphenol A, flowability, chemical resistance and oil resistance are insufficient and furthermore it is very expensive. Japanese Patent Kokai (Laid-open) No. 10-101786 discloses a polycarbonate resin derived from 9,9-bis(4-(2-hydroxyethoxy)phenyl)fluorene and bisphenols. Although the polycarbonate resin has lower birefringence than that of a polycarbonate resin derived from bisphenol A, flowability, chemical resistance and oil resistance are insufficient and photoelastic constant is not sufficiently low.
Thus, Japanese Patent Application No. 2003-039586 suggests a copolymerization polycarbonate resin derived from 9,9-bis(4-(2-hydroxyethoxy)phenyl)fluorene and aliphatic diols. Although the resin exhibits sufficiently low birefringence, excellent flowability and low photoelastic constant, chemical resistance and oil resistance are not sufficient.
Therefore, a low price polycarbonate resin excellent in chemical resistance and oil resistance having low birefringence has been required.
On the other hand, a polarizing sheet has been widely applied to the field of optical materials such as a sun glass and a goggle to require anti-glare since it exhibits excellent anti-glare. The polarizing sheet has a structure adhered a transparent sheet to one side or both sides of a polarizer. As the polarizer, for example, there is used a polarizing film in which iodine or a dichroic dye is adsorbed to a polymer film including, typically, polyvinylalcohol or derivatives thereof and the film to be thus obtained is stretch-oriented to uniaxis. As the transparent sheet, cellulose sheets, acrylic sheets and polycarbonate sheets have been used, among which polycarbonate sheets have been widely used in the field to require impact resistance and heat resistance.
Polycarbonate herein means a conventional, low price and readily obtainable polycarbonate resin derived from bisphenol A. However, the polycarbonate resin derived from bisphenol A, as described above, has a defect that birefringence and photoelastic constant are large.
According to studies by the inventors of the present invention, they have found that when a transparent film comprising a polycarbonate resin derived from bisphenol A is adhered to both sides of a polarizing film to form a polarizing sheet and the polarizing sheet thus obtained is vacuum formed, pressure formed or press formed into a curved surface shape, optical strain is caused in a portion of the curved surface due to stress strain, so that remarkable bad influence to disturb polarization occurs.
When a curved surface-shaped molded article with such optical strain is seen from its oblique side, color ununiformity of rainbow color is observed. Further, when the curved surface polarizing sheet is observed in the state overlapped to a flat polarizing sheet disposed so as for each polarizing axes to form orthogonal position to each other, so-called “discoloration” in which a light is transmitted and colored interference fringe are observed. Further, when the curved surface polarizing sheet is observed in the state overlapped to a flat polarizing sheet disposed so as for each polarizing axes to become parallel to each other, coloration different from a color of the polarizing film is observed in a portion of the polarizing sheet and colored interference fringe is observed.
For example, Japanese Patent Kokai (Laid-open) No. 9-5683 discloses a convex lens shaped polarizing sheet for spectacle in which a polycarbonate resin sheet with a retardation value [defined as birefringence (Δ n)×thickness (d)] of 3000 to 6000 nm is laminated on at least one side of a polarizing film and curve surface-processing is performed. The publication describes that a polycarbonate resin sheet with a retardation value of at least 3000 nm derived from bisphenol A is adhered to both sides of a polarizing film to make a polarizing sheet and the polarizing sheet is cut into a round shape and then curve surface-processed into a convex lens shape by pressure forming and when the a convex lens shaped polarizing sheet is observed from its oblique direction, no color ununiformity is observed. This process has been applied to actual production and is an available process. However, the process causes problems in workability that orientation treatment by stretching is required in order to secure a retardation value of a polycarbonate resin sheet and furthermore it is necessary to accord the orientation axis to the axis direction of the polarizing sheet. Further, the polycarbonate resin sheet has a defect that shrinkage occurs with heating in secondary processing.
Japanese Patent Kokai (Laid-open) No. 2001-305341 discloses a polarizing sheet adhered a polycarbonate sheet with a retardation value of 300 nm or below and a thickness of 0.05 to 0.25 mm to one side or both sides of a polarizing film. In the publication, a transparent protective sheet composed of a polycarbonate resin derived from bisphenol A is prepared according to a cast method and then the transparent protective sheet is adhered to both sides of a polarizing film to prepare a polarizing sheet and polarizing performances of the polarizing sheet has been evaluated. However, in the publication, polarizing performances in case of not performing curve surface-processing for a polarizing sheet with a transparent protective sheet composed of a polycarbonate resin derived a bisphenol A have been merely evaluated. As a result of studies by the inventors of the present invention, the polarizing sheet was cut into a round shape and then curve surface-processed into a convex lens by vacuum forming to prepare a convex lens shaped polarizing sheet and when the convex lens shape polarizing sheet was seen from its oblique side, color ununiformity of rainbow color was observed. Further, when this curved surface polarizing sheet was observed in the state overlapped to a flat polarizing sheet so as for each polarizing axes to form orthogonal position to each other, so-called “discoloration” in which a light is transmitted and colored interference fringe were observed. Further, when the curved surface polarizing sheet was observed in the state overlapped to a flat polarizing sheet disposed so as for each polarizing axes to become parallel to each other, coloration different from a color of the polarizing film was observed in a portion of the polarizing sheet and colored interference fringe was observed. This means that even when curve surface-processing is performed, optical properties of the product are still insufficient.
After the completion of curve surface-processing, optical strain is caused. In other words, when the curved surface polarizing sheet is seen from its oblique side, color ununiformity of rainbow color is observed; when the curved surface polarizing sheet is observed in the state overlapped to a flat polarizing sheet disposed so as for each polarizing axes to form orthogonal position to each other, so-called “discoloration” in which a light is transmitted and colored interference fringe are observed or when the curved surface polarizing sheet is observed in the state overlapped to a flat polarizing sheet disposed so as for each polarizing axes to become parallel to each other, coloration different from a color of the polarizing film is observed in a portion of the polarizing sheet and colored interference fringe is observed. This is due to large birefringence of the polycarbonate resin derived from bisphenol A, i.e., large intrinsic birefringence, large orientation distribution function or large photoelastic constant.
Therefore, as a transparent protective sheet of a polarizing film, various resins with low birefringence have been tested. However, as a result of studies, the inventors have found that a transparent protective sheet composed of an amorphous polyolefin as typical low birefringence resin is processed into a polarizing sheet and when the polarizing sheet thus obtained is curve surface-processed into a convex lens shape, optical strain which is not observed in a flat polarizing sheet is caused, i.e., when the curved surface polarizing sheet is seen from its oblique side, color ununiformity of rainbow color is observed; when the curved surface polarizing sheet is observed in the state overlapped to a flat polarizing sheet disposed so as for each polarizing axes to form orthogonal position to each other, so-called “discoloration” in which a light is transmitted and colored interference fringe are observed or when the curved surface polarizing sheet is observed in the state overlapped to a flat polarizing plate disposed so as for each polarizing axes to become parallel to each other, coloration different from a color of the polarizing film is observed in a portion of the polarizing sheet and colored interference fringe is observed.
Thus, a polarizing sheet in which optical strain is not substantially caused in curve surface-processing and optical properties including appearance are very excellent has been required. Such polarizing plate can be suitably applied to various optical uses including anti-glare materials.